Device and Method for Irradiating Tissue with Light Pulses

ABSTRACT

The invention relates to a device ( 1 ) for irradiating tissue (G) with light pulses (L), comprising a housing ( 2 ), at least one light source ( 3 ) for emitting the light pulses (L) with a wavelength (λ) of from 600 nm to 660 run, a modulator ( 4 ) and a power stage ( 6 ) for generating the light pulses (L), and with an activating element ( 5 ). For creating a device ( 1 ) which is as small, as cost-efficient and as effective as possible, by which as good a therapy success as possible is achieved in various applications, the modulator ( 4 ) is designed for generating the light pulses (L) with a pulse frequency (f) of from 1 to 10 Hz, and the power stage ( 6 ) is designed for emitting the light pulses (L) with an energy which causes breaking up of the photosensitizer in the photodynamic therapy and evokes a frequency doubling or a two-photon absorption (TPA) in the tissue (G) when treating inflammations without a sensitizer.

The invention relates to a device for irradiating tissue with lightpulses, comprising a housing, at least one light source for emitting thelight pulses with wavelengths of from 600 nm to 660 nm, a modulator anda power stage for generating the light pulses, and with an activatingelement.

Furthermore, the present invention relates to a method for irradiatingtissue with light pulses emitted by light sources and having wavelengthsof between 600 nm and 660 nm.

In principle, the present invention is directed to the irradiation ofhuman tissue, in particular of the skin and of the regions locatedtherebelow. However, also applications are possible in which, e.g. viaan endoscope or the like, the tissues of inner organs are irradiatedwith light and diseases are treated accordingly. Basically, also anapplication on animals is possible.

Devices and methods for irradiating tissue with light for differentpurposes are known. By means of phototherapeutic methods, certain skindiseases can be alleviated or cured using an irradiation with light of aspecial wavelength or with combinations of various wavelengths. Forinstance, skin diseases, such as, e.g., psoriasis, can be treated byirradiation with ultraviolet light. The photodynamic therapy (PDT)refers to a method for treating tumours and other changes of tissue withlight in combination with a light-sensitive substance, a so-calledphotosensitizer. The photosensitizer administered to the patient isselectively enriched in the tumour. By irradiating with light of asuitable wavelength, toxic substances are produced by photophysicalprocesses, which substances specifically damage the tumour. What isdetrimental in this case are the side effects of the photosensitizer.

WO 2006/005088 A1, e.g., describes a device for the photodynamictreatment of diseases of the tissue by using a power light-emittingdiode in the red light spectrum, and the effect of the irradiation onthe patient is detected by means of a sensor. Thereby lower powerdensities can be used and the thermal load on the patient can bereduced. However, comparatively large cooling elements are required forconducting away the relatively high thermal dissipation losses which,nevertheless, do occur.

U.S. Pat. No. 5,698,866 A shows a device for photodynamic therapy withan array of light-emitting diodes, which allows for a precise regulationof the exposure to light and a precise dosimetry using a sensor formedby a fibre-optic system.

WO 02/062420 A1 also shows a device for the photodynamic therapy, inwhich sensors are provided which are employed for controlling theduration of irradiation. The device has a comparatively complex andlarge construction and, therefore, is only suitable to be used inhospitals or doctor's offices.

WO 97/35635 A2 describes an apparatus for the treatment of biologicaltissue by means of laser light with preferred wavelengths of 1064 nm and2500 nm. What is detrimental is that the degree of absorption of abiological tissue at such wavelengths is relatively low and, thus, veryhigh power densities must be used for achieving an effect, which powerdensities in turn are painful for the patient.

In all the photodynamic therapy methods, the photosensitizer in mostinstances has undesired side effects and negative impacts.

U.S. Pat. No. 6,736,807 B2 shows a depilating device with the use oflaser light. For a lasting destruction of the roots of the hair,comparatively high power densities must be used. The wavelengths used donot penetrate very far into the tissue to be treated, and therefore atreatment of deeper tissue regions is not possible with such laser lightsources.

Moreover, methods and devices for stimulating acupuncture points bymeans of laser light are known. DE 101 28 629 A1, e.g., describes alight-emitting device designed as a skin patch, in which light pulsesgenerated by a laser diode are used for the acupuncture treatmentinstead of the pricks generated by acupuncture needles.

The present invention has as its object to provide a device forirradiating tissue with light, which device is to be as small, ascost-efficient and as effective as possible, as well as a method whichresults in as great a therapy success as possible with as short aduration of treatment and as little pain as possible for the patient andwhich, moreover, lends itself to different therapy applications. Inparticular, the present device and the present method shall be suitablefor treating inflammatory tissue diseases and entail as slight burdensand side-effects for the patient as possible. Yet, the device shall alsobe suitable for a use by the patient at home and, accordingly, should beas handy, as simple and as safe to be operated as possible.Disadvantages of the prior art shall be avoided or, at least, reduced.

The object according to the invention is achieved by an above-indicateddevice for irradiating tissue, wherein the modulator is designed forgenerating the light pulses with a pulse frequency of from 1 to 10 Hzand the power stage for generating the light pulses is designed with anenergy which causes a two-photon absorption or a frequency doubling inthe irradiated tissue when treating inflammations without sensitization,or which causes a breaking up of a photosensitizer in the photodynamictherapy, respectively. The present device for irradiating tissue withlight pulses is excellently suitable for treating a number of skin andtissue diseases, respectively, in particular inflammatory diseases, suchas, e.g., psoriasis, neurodermatitis, mycoses, or also for the treatmentof melanomas, the latter with the addition of suitable photosensitizers.By pulsing the light with 1 to 10 Hz, any pain can be clearly reduced atstill relatively high power densities as compared to conventionalirradiation devices. The reason for the selection of the pulse frequencyresides in the effect of that time which is required in order totransport away destroyed cells or cell parts via the blood. Tests have,e.g., shown that at least 0.2 seconds are required for those parts whichhave been destroyed by the light to be transported away via the blood.In case of a higher pulse frequency, or in case of a lower pulsefrequency, respectively, it would not be possible for the material to betransported away to be removed by the blood in time before the nextlight pulse, manifesting itself as a reduced depth of penetration and aspain. Moreover, due to the pulsing of light, the heat development isreduced and, thus, also the pain sensation due to the influence of heatis impossible. Apart from the pulse frequency used, also the energy ofthe light pulses is essential which, according to the invention, ischosen such that a so-called two-photon absorption or a doubling offrequency will occur within the tissue. At two-photon absorption (TPA),two photons are at the same time absorbed by an atom or molecule in theirradiated tissue and, at the same time, the atom or molecule is therebyconverted into an excited state. Due to non-linear processes, a doublingof the frequency, or a halving of the wavelength of the irradiatinglight occurs, which, in the instant case, causes the generation of aradiation in the UVB range (i.e. at a wavelength k in the range of from300 nm to 330 nm). The UVB radiation may cause a destruction ofsubstances that are responsible for the disease of the tissue. In theliterature, particularly leukotriene B₄ (LTB4) or its derivatives, thatis a hormone-like substance occurring in connection with allergic andinflammatory reactions of the body, are mentioned (B. Millar et al.: Astudy of the photodegradation of leukotriene B₄ by ultravioletirradiation (UVB, UVA), British Journal of Dermatology (1989) 120, pp.145-152). By the two-photon absorption or frequency doubling, the activesubstance leukotriene B₄ (LTB4) or its derivatives can be inhibited orconverted and, thus, the disease can be treated and/or cured,respectively. For the occurrence of the two-photon absorption orfrequency doubling within the tissue, comparatively high power densitiesare required which must be adapted to the respective application. Testshave shown that two-photon absorption or frequency doubling aremeasurable within the tissue. Thus, for treating certain diseases, thelight dose required can be determined from experience and, subsequently,depending on the pulse frequency used and the pulse duty factor used,the power density of the light sources required for two-photonabsorption can be determined. Compared to known devices, it is possiblewith the subject irradiation device to obtain an optimum treatmentresult by, e.g., direct UVB irradiation or by photosensitizers within avery short duration of treatment and without any pain for the patientand, as a rule, without any side effects. By using red light in thewavelength range indicated it is, therefore, possible to attain anoptimum absorption of the light radiation within the tissue, wherein atthe site of the disease, i.e. within the tissue, UVB radiation isgenerated which leads to the inhibition or destruction of the mediatorsresponsible for the disease. If the tissue were directly irradiated withlight in the UVB range, the penetration depth would be very low, sincetissue consists mainly of water which is not transparent for the UVBradiation. In order to achieve an effect within the tissue nonetheless,the power densities of the light sources therefore would have to bechosen appropriately high which, in turn, would cause pain on account ofthe heat occurring. Moreover, the direct irradiation with UVB lightwould have further disadvantages due to the risk of cancer.

According to a further feature of the invention it is provided for themodulator for generating the light pulses to be designed with a pulseduty factor of ≦0.6. Tests have shown that an upper limit of 60% is thebest for the pulse duty factor. Theoretically, the lower limit can bechosen deliberately, yet nevertheless it is defined by the fact that thetreatment time should remain within reasonable limits. If the pulse dutyfactor were chosen very small, the treatment time for transmitting thedose of light required for the disease to be treated would have to bechosen to be correspondingly long. Short treatment times are, of course,advantageous for the patient, wherein e.g. 30 to 60 minutes can beindicated as the upper tolerance limit.

The power stage for generating the light pulses preferably is designedwith a peak power density of ≧50 mW/cm², based on the pulse duty factorΔT/T. At these values, optimum results could be achieved.

According to a further feature of the invention it is provided that theat least one light source is fastened to the housing such that the atleast one light source can be directly arranged on the surface of thetissue to be irradiated. By such a design of the irradiation device,deeper regions of the tissue can be treated with light. For instance,joints can be irradiated with light for treating inflammatoryarthropathies.

If several light sources are arranged along a line, regions, such as,e.g., joint spaces, yet also the tissue between the ribs, can be treatedspecifically. As required, the light sources can be arranged indifferent patterns.

As an alternative to the above-mentioned embodiment, also spacerelements can be provided for creating a defined distance of the at leastone light source from the surface of the tissue to be treated. Thisembodiment is particularly suitable for irradiating the skin and tissueregions in the immediate vicinity of the skin surface. The space betweenthe light sources and the surface of the tissue to be treated isadjusted accordingly to the disease to be treated, on the one hand, andalso to the light sources used, on the other hand.

In order to be able to use the device also for different applications,it is also possible to design the spacer elements adjustable. Variousconstructions can be employed for providing the adjustability. Moreover,by changing the distance between light sources and the skin surface, theenergy density can be changed, with a simultaneous change of the areabeing irradiated.

With the embodiment of the device in which the light sources arearranged at a distance from the surface of the tissue to be treated, itmay be advantageous to arrange a lens for bundling the light rays infront of the at least one light source, or to integrate the lens in thelight source, e.g. in the light-emitting diode.

If there are several light sources, the latter are arranged in the raydirection preferably at an inclination relative to one another, so thatall the light rays are directed at the desired region to be treated. Dueto the bundling of the light rays, the power density of the lightsources can be reduced to a necessary minimum and, thus, also the powerloss of the light sources manifested as a heat development can bereduced. The result is a handy construction of the device which allowsfor wide applications also by the patients themselves, due to whichfrequent trips to the hospital or to the doctor can be omitted.

If according to a further feature of the invention, a sensor is providedfor detecting the light rays reflected from the surface of theirradiated tissue, the amount of light absorbed by the tissue can, onthe one hand, be estimated and used, e.g., for controlling theirradiation device, or also the success of the therapy can be quantifiedand the duration of treatment can be fixed. On account of theirradiation, usually the composition of the tissue changes, expressingitself in a changed absorption ability of the tissue. Thus, via theintensity of the reflected light, the quality of the treatment can bejudged and the optimum duration of treatment can be fixed.

Advantageously, the sensor is formed by an optical fiber and aphotosensitive element, the free end of the optical fiber being arrangedat a defined distance from the surface of the tissue, and the other endof the optical fiber being connected to the photosensitive element. Thelight reflected by the tissue is conducted through the optical fiber tothe photosensitive element. For detecting the reflected light, merelythe particularly thin optical fiber is necessary which hardly influencesthe light rays of the light source.

Advantageously, the distance of the free end of the optical fiber ischangeable so as to provide for a calibration and adaptation of themeasurement of the radiation reflected by the skin surface.

Furthermore, a separate reference light source and a sensor fordetecting the reference light radiation reflected by the tissue can beprovided.

In doing so, the wavelength of the reference light source is optimallyadjusted to the respective fields of use. In this respect, the use ofUVB radiation having a wavelength of between 280 nm and 320 nm fordetermining the success of treatment has been particularly suitable. Thepower density of the reference light source is particularly low comparedto the power density of the light sources, so that the UVB irradiationcannot exert any damaging effect on the tissue. Via the measurement ofthe absorption ability of UV radiation by the tissue being treated, thesuccess of the treatment can be detected and quantified, respectively,in a suitable manner.

If the sensor is connected to an evaluation unit, the measured,reflected light can be evaluated accordingly and, e.g., quantified.

If the evaluation unit is connected to the modulator for generating thelight pulses, a closed control circuit can be formed, wherein parametersof the light pulses, such as power density, pulse frequency, pulse dutyfactor, pulse duration or the like can be regulated as a function of themeasured, reflected light.

Advantageously, the modulator for generating the light pulses isdesigned with a pulse frequency of 2.5 Hz and with a pulse duty factorof 0.5. As already mentioned above, with a photodynamic therapy,approximately 0.2 seconds are required for removing the cell componentsdestroyed during the irradiation via the bloodstream. With theparameters indicated, the pulse duration will exactly correspond tothese 0.2 seconds.

Since the subject device shall also be suitable to be used by thepatients themselves, it is advantageous if there are no or nosubstantial adjustment possibilities and if the required parameters aredefinitely and non-changeably pre-adjusted. It may, however, beadvantageous for a memory to be provided for storing various values forthe pulse frequency, the pulse duty factor and the power density as wellas an operating element for selecting the desired values from thememory. In this way, various adjusted positions can be stored in thedevice, from which the operator of the device chooses the desiredcombination with the help of the operating element without the risk ofmaladjustments and, thus, a false treatment.

Advantageously, at least one light source is formed by at least onelight-emitting diode. The light-emitting diode can have an integratedlens or it may also be used without a lens. At present, light-emittingdiodes in the wavelength range indicated, in particular in the range ofbetween 637 nm and 643 nm, can be obtained at particularly reasonableprices.

If batteries are provided for the voltage supply, the device can be usedindependently of an external voltage supply. It is then advantageous touse rechargeable batteries so as to make it possible to use the deviceoften without having to change the batteries.

In order to prevent a damage to the eyes of a person by the relativelyintensive red light radiation of the lightsources, a means for detectinga contact of the light sources or of a spacer element with the surfaceof the tissue to be irradiated may be provided. By such a detectionmeans which may, e.g., be formed by a microswitch or by an opticalelement, an activation of the light sources will become possible only ifthe device is applied at the desired tissue region.

For this purpose, the detection means preferably is connected to themodulator so that an activation of the modulator is allowable only if acontact of the light sources or of a spacer element with the surface ofthe tissue to be irradiated has been recognized.

Even though the device is to be constructed as simple and robust aspossible, a display for displaying the operating state or certainparameters may be provided. The display may be formed in the simplestmanner by one or more light-emitting diodes or by a seven segmentdisplay up to an LCD display.

Advantageously, the housing is designed to be splash-proof so that thecomponents contained therein are appropriately protected.

To protect the light sources and the power stage from over-heating, theymay be connected to an appropriately dimensioned cooling element. For anoptimum heat transport, also appropriate thermally conductive materials,such as, e.g., thermally conductive paste, may be used.

The object according to the invention is also achieved by anabove-indicated method for irradiating tissues with light pulses,wherein the light pulses are emitted with a pulse frequency of from 1 to10 Hz, and the energy of the light radiation is adjusted for evoking atwo-photon absorption or frequency doubling in the irradiated tissue. Asregards the advantages attainable thereby and the further methodcharacteristics according to the invention, reference is made to theabove description of the device and the appended drawings and theirdescription.

Accordingly, the present invention will be explained in more detail byway of the accompanying drawings.

Therein,

FIG. 1 shows a schematic illustration elucidating the two-photonabsorption or frequency doubling within the tissue;

FIG. 2 shows the spectrum of the light intensity occurring within thetissue;

FIG. 3 shows the light pulses as a function of time;

FIG. 4 shows a block diagram of an embodiment of a device according tothe invention for irradiating a tissue with light pulses;

FIGS. 5A and 5B show two views of an embodiment of an irradiationdevice;

FIG. 6 shows detail VI of FIG. 5B in an enlarged illustration;

FIGS. 7A and 7B show two views of a further embodiment of an irradiationdevice; and

FIG. 8 shows the temporal course of the intensity of thetissue-reflected light, which temporal course is highly dependent on thetype of the diseased tissue, during a treatment.

FIG. 1 shows a scheme for elucidating the two-photon absorption (TPA) orfrequency doubling occurring in tissue G. Tissue G is irradiated withlight pulses L of the wavelength λ of between 600 nm and 660 nm. Redlight of this wavelength λ is in the so-called water window and,therefore, is particularly suitable, since at this wavelength λ human oranimal tissues are particularly transparent due to their high watercontent and, thus, very much light energy can be absorbed by thephotosensitizer in tissue G. In the inflamed tissue (not in tumours),there are so-called leukotrienes which increasedly occur in allergic andin-flammatory reactions. In particular, leukotriene B₄ (LTB4) or itsderivatives are being mentioned in the context of inflammatory diseasesof the tissue G. If the effect of the leukotriene B₄ (LTB4) or itsderivatives is inhibited, the disease can be alleviated or cured. By anappropriate energy of the light pulses L, due to a frequency doubling ortwo-photon absorption (TPA), a frequency doubling or wavelength halvingoccurs in the leukotriene B₄ (LTB4) and/or its derivatives, whichfinally leads to an inhibition and/or destruction of the leukotriene B₄(LTB4) or its derivatives. What is responsible for this in any event isa non-linear effect, in which a doubling of the frequency of theirradiating light pulses L occurs. This is indicated in FIG. 1 by lightwaves in tissue G by the wavelength λ/2, i.e. in the range between 300nm and 330 nm, i.e. in the UVB range. Tissue G, thus, is irradiated withred light having a wavelength λ of from 600 nm to 660 nm, and theleukotriene B₄ (LTB4) is inhibited or converted by the frequencydoubling or two-photon absorption (TPA) occurring.

As can be seen in the spectrum according to FIG. 2, a certain powerdensity p of the measured light could be recorded at half the wavelength λ/2 of the irradiating light pulses L by means of measurementtechnique, which is not the second harmonic of the light radiation ofthe light source.

FIG. 3 shows the essential parameters of the light pulses L as afunction of time t. Accordingly, the light pulses L are repeated with apulse frequency f, or a period duration T=1/f, and a pulse duty factorΔT/T of ≦0.6, or 60%, respectively, is selected. The peak power density{circumflex over (p)} preferably is ≧0.05 Watt/cm², based on the pulseduty factor ΔT/T.

FIG. 4 shows a block diagram of an embodiment of the device 1 accordingto the invention for irradiating tissue G with light pulses L,comprising a housing 2 with at least one light source 3 for emittinglight pulses L with a wavelength λ of from 600 nm to 660 nm, a modulator4 for generating the light pulses L, and an activating element 5 foractivating the irradiation device 1. The modulator 4 activates a powerstage 6 with the desired pulse frequency f and the respective pulse dutyfactor ΔT/T, so that the light sources 3 will be supplied with acorresponding current. The light sources 3 preferably are light-emittingdiodes which can be purchased at particularly reasonable prices and insmall designs.

To supply the components of the device 1 with electric energy, a voltagesupply 7 is provided which may be formed by a power adapter 8 andterminals 9 for connection to a power outlet or by a—preferablyrechargeable—battery 10. Via a setting member 11, parameters of thelight pulses L, such as, e.g., pulse frequency f, pulse duty factor ΔT/Tor the peak power density {circumflex over (p)} can be changed. However,an embodiment of the device 1, in which as far as possible theparameters cannot be changed by the patients, is preferred. In this way,a false operation and, thus, a false treatment with the device 1 isprevented. However, a memory 12 may be provided in which differentvalues for the pulse frequency f, the pulse duty factor ΔT/T and thepeak power density {circumflex over (p)} can be stored, which can becalled up and adjusted via an operating element 13. For instance,different parameters can be stored in memory 12 for treating differentdiseases.

Via a sensor 14, the light irradiation reflected by tissue G may bedetected and supplied to an evaluation unit 15, e.g., so as to be ableto quantify the light irradiation absorbed by tissue G and the successof the therapy. If the evaluation unit 15 is connected to the modulator,a regulation of the parameters of the light pulses L can be carried outdue to the reflected light irradiation measured. A reference lightsource 16 may be provided to which the sensor 14 is adapted with regardto the wavelength λ. In this case, a wavelength λ in the UV-range isparticularly suitable, since the absorption ability of the tissue in theUV range is changed in dependence on the treatment and, thus, from thereflected light irradiation conclusions can be drawn regarding thesuccess of the treatment.

The device 1 according to the invention may be of a particularly smalldesign so that an ambulant use or a use by the patients at their homesis possible. Of course, the size of the irradiation device 1 will beadapted to the size of the tissue area to be treated. For the treatmentof larger body regions it is, of course, also possible to usefloor-mounted appliances.

FIGS. 5A and 5B show various views of an embodiment of the irradiationdevice 1, wherein two light sources 3 are arranged at a defined distanced from the surface O of the tissue G to be treated. For bundling thelight rays, lenses 17 are arranged in front of the light sources 3 and,moreover, the two light sources 3 are arranged to be inclined towardseach other in the direction of the rays. The distance d of the lightsources 3 to the surface O of the tissue G to be treated is defined by aspacer element 18 which, in the example illustrated, is realized by acylindrical element having appropriate recesses 19 at its side facingthe tissue G. By means of the recesses 19, an air supply is ensured andoverheating of the tissue G under the device 1 is prevented. The spacerelements 18 may also be designed to be adjustable so as to achieve anadjustment of the distance d of the light sources 3 to the surface O ofthe tissue G to be treated (not illustrated). This adjustability of thespacer elements 18 may, e.g., be realized by a screw thread or by otherconstructions.

The most important components of the device 1 are arranged withina—preferably splash-proof—housing 2, at which cooling elements 20 may bearranged for conducting away the thermal dissipation loss. Inparticular, the cooling elements 20 are in thermal contact with thelight sources 3 and the power stage 6. Via an activation element 5, thedevice 1 is switched on and off.

Via a sensor 14, the light radiation reflected by the tissue G can berecorded and evaluated. As illustrated in FIG. 6 on an enlarged scale,the sensor 14 is, e.g., formed by an optical fiber 21 having aninsulation 22 which, preferably, projects somewhat beyond the free end23 of the optical fiber 21 so that only the light reflected by thetissue G is detected. The other end of the optical fiber 21 (notillustrated) is connected to a suitable photosensitive element withinthe housing 2, and the incoming light radiation is appropriatelyevaluated. In order to enable an adaptation and calibration of thedevice, the distance d_(S) of the sensor 14 from the surface O of thetissue G may be changeable. In the arrangement of two light sources 3illustrated, the sensor 14 preferably is located between the lightsources 3 at the centre of the cone of light obtained.

Furthermore, a means 26 may be provided for detecting a contact of thelight sources 3 or of the spacer element 18 with the surface O of thetissue G to be irradiated, so as to allow for an activation of the lightsources 3 only with the device 1 applied and to prevent damage to theeyes of the patient or of other persons by the intensive red lightradiation of the light sources 3. The detection means 26 may, e.g., beformed by a microswitch or by a photosensitive element that is connectedto a part of the electronic circuit of the device 1.

Finally, a display 27 may be provided, which displays the operatingstate of the batteries 10 or the like. Instead of a display 27 formed bya light-emitting diode or the like, also an LCD-display may be providedwhich may provide the user of the device 1 with more information.

FIGS. 7A and 7B show a further embodiment of the device 1 forirradiating tissue G with light pulses L, wherein several light sources3 are arranged on a housing 2 along a line. On the housing 2, a handle24 may be arranged in which, e.g., the batteries for supplying thedevice 1 with electric energy may be arranged. Via a lid 25, thebatteries can be exchanged. The device 1 is switched on and off via theactivating element 5. This embodiment of the device 1 is suitable for adirect application of the light sources 3 on the surface O of the tissueG to be treated so as to attain greater penetrating depths of the lightrays into the tissue G. By arranging several light sources 3 along aline, joint spaces located in deeper tissue regions can be reached andappropriately treated.

FIG. 8 shows a typical course of the intensity I_(R) of the lightreflected by the tissue G, which light increases after the onset of thetreatment up to a peak value I_(R) and subsequently drops comparativelysteeply. Experience has shown that the treatment can be finished when alower limit value I_(R), of the intensity of the reflected lightradiation has been reached. The resultant duration of treatment t_(B)should not exceed 30 to 60 minutes so as to be acceptable to thepatients.

The present device 1 for irradiating tissue G with light pulses L couldbe particularly successfully used in case of psoriasis and otherinflammatory skin diseases. No pain was sensed during the treatment, andalready after a few treatments a substantial improvement or even a curecould be achieved. Also with malignant skin diseases, such as, e.g.,basaliomas, the present irradiation device 1 can be successfullyemployed while simultaneously using photosensitizers.

Even with metastasising and highly dangerous melanomas, there arechances for a therapy with this device 1 if a suitable sensitizer couldbe found.

1.-24. (canceled)
 25. A device for irradiating tissue with light pulses,comprising a housing, at least one light source for emitting the lightpulses with a wavelength of from 600 nm to 660 nm, a modulator and apower stage for generating the light pulses, and with an activatingelement, wherein the modulator for generating the light pulses isdesigned with a pulse frequency of from 1 to 10 Hz, and in that thepower stage for generating the light pulses is designed with a peakpower density of ≧50 mW/cm², based on the pulse duty factor, resultingin an energy of the light pulses which causes a two-photon absorption ora frequency doubling in the irradiated tissue.
 26. The device of claim25, wherein the modulator is designed for generating the light pulseswith a pulse duty factor of ≦0.6.
 27. The device of claim 25, whereinthe at least one light source is fastened to the housing such that theat least one light source can be arranged directly on the surface of thetissue to be irradiated.
 28. The device of claim 27, wherein severallight sources are arranged along a line.
 29. The device of claim 25,wherein spacer elements are provided for producing a defined distance ofthe at least one light source from the surface of the tissue to betreated.
 30. The device of claim 29, wherein the spacer elements aredesigned to be adjustable.
 31. The device of claim 29, wherein a lensfor bundling the light rays is arranged in front of the at least onelight source or integrated therein.
 32. The device of claim 29, whereinseveral light sources are arranged to be inclined relative to oneanother in ray direction.
 33. The device of claim 25, wherein a sensorfor detecting the light rays reflected by the surface of the irradiatedtissue is provided for measuring the absorption ability of the tissue.34. The device of claim 33, wherein the sensor is formed by an opticalfiber and a photosensitive element, wherein the free end of the opticalfiber is arranged at a defined distance from the surface of the tissue,and the other end of the optical fiber is connected to thephotosensitive element.
 35. The device of claim 34, wherein the distanceof the free end of the optical fiber from the surface of the tissue ischangeable.
 36. The device of claim 25, wherein a reference light sourceand a sensor for detecting reference light radiation reflected by thetissue are provided.
 37. The device of claim 36, wherein the referencelight source is designed for emitting light with a wavelength of between280 nm and 320 nm and the sensor is designed for detecting light with awavelength of from 280 nm to 320 nm.
 38. The device of claim 33, whereinthe sensor is connected to an evaluation unit.
 39. The device of claim38, wherein the evaluation unit is connected to the modulator.
 40. Thedevice of claim 25, wherein the modulator is designed for generating thelight pulses with a pulse frequency of 2.5 Hz and a pulse duty factor of0.5.
 41. The device of claim 25, wherein a memory for storing variousvalues for the pulse frequency, the pulse duty factor and the powerdensity and an operating element for selecting the desired values fromthe memory are provided.
 42. The device of claim 25, wherein the atleast one light source is formed by at least one light-emitting diode.43. The device of claim 25, wherein batteries are provided for supplyingvoltage.
 44. The device of claim 25, comprising a detector that detectscontact of the light sources or of a spacer element with the surface ofthe tissue to be irradiated.
 45. The device of claim 44, wherein thedetector is connected to the modulator.
 46. The device of claim 25,wherein a display is provided.
 47. The device of claim 25, wherein thehousing is designed to be splashproof.
 48. The device of claim 25,wherein the light sources and the power stage are connected to a coolingelement.
 49. A method for irradiating tissue comprising: obtaining adevice of claim 25; and using the device to irradiate tissue.
 50. Amethod for irradiating tissue with light pulses emitted from lightsources and having wave lengths of between 600 and 660 nm, wherein thelight pulses are emitted with a pulse frequency of from 1 to 10 Hz andwherein the light pulses are emitted with a peak power density of ≧50mW/cm², based on the pulse duty factor, and the energy of the lightradiation is adjusted for causing a two-photon absorption or a frequencydoubling in the irradiated tissue.
 51. The method of claim 50, whereinthe light pulses are emitted with a pulse duty factor of below 0.6. 52.The method of claim 50, wherein the light sources are arranged directlyon the surface of the tissue to be treated.
 53. The method of claim 50,wherein the light sources are arranged at a defined distance from thesurface of the tissue to be treated.
 54. The method of claim 53, whereinthe light pulses are bundled.
 55. The method of claim 50, wherein formeasuring the absorption ability of the tissue being treated, theintensity of the light rays reflected by the surface of the tissue beingtreated is measured.
 56. The method of claim 55, wherein the intensityof the light rays reflected by the surface of the tissue being treatedare measured at a wavelength of from 280 nm to 340 nm.
 57. The method ofclaim 50, wherein for measuring an effect of the irradiation, light rayswith a wave length in the range of from 280 nm-320 nm are emitted to thetissue to be treated, and the intensity of the light rays with a wavelength in the range of 280 nm-320 nm reflected by the surface of thetissue being treated is measured.
 58. The method of claim 55, whereinthe intensity of the light reflected from the tissue being treated ismeasured at a defined distance from the surface of the tissue.
 59. Themethod of claim 55, wherein the temporal course of the intensity of thelight reflected by the tissue is detected and the course of theintensity is employed for regulating the duration of treatment.
 60. Themethod of 50, wherein the light pulses are emitted with a pulsefrequency of 2.5 Hz and a pulse duty factor of 0.5.
 61. The method ofclaim 50, wherein the energy of the light pulses is adjusted such thatthe duration of treatment ≦30 minutes.
 62. The method of claim 50,wherein different values for the pulse frequency, the pulse duty factorand the power density are stored and selected before the treatment. 63.The method of claim 50, wherein a photosensitizer is used which reactswith the light pulses.
 64. The method of claim 50, wherein the lightsources are deactivated as soon as they are turned away from the tissueto be irradiated.
 65. The method of claim 50, wherein the pulsefrequency, the pulse duty factor, the power density, the energy densityor the duration of treatment are displayed.